The present invention relates to an apparatus and a method for controlling a diesel engine.
There is known an earlier diesel engine of a direct fuel injection type where a combustion temperature in a combustion chamber is lowered by introducing heavy EGR, known as exhaust gas recirculation, back into the combustion chamber. Under this approach, an ignition delay period is largely prolonged so as to build a heat release pattern with one-step combustion shape (the ignition delay period is longer than a fuel injection period) called a low temperature-premixed combustion, and thereby, NOx and smokes are reduced at the same time.
In this engine, the premixing is further expanded by dispersing fuel into the entire combustion chamber due to formation of a high swirl in the combustion chamber and a cylindrical shape of the combustion chamber (see Japanese Unexamined Patent Publication No. 8-86251).
However, in the above diesel engine, the ignition delay period is too long compared to the fuel injection period either under relatively colder engine conditions or a lowered compression ratio.
As a result, when time from a fuel injection completion to an ignition start becomes too long, fuel is dispersed too much into the entire combustion chamber and an equivalent ratio of fuel to air in the vicinity of a cylinder center (in a piston cavity) becomes extremely lean. Therefore, an emission quantity of unburned hydrocarbons (HC) is increased.
One aspect of the invention provides an apparatus for controlling a diesel engine where a combustion temperature in a combustion chamber is lowered, and an ignition delay period is largely prolonged so as to build a heat release pattern with one-step combustion shape, as well as an equivalent ratio distribution in the combustion chamber at an ignition start is controlled such that the equivalent ratio in the vicinity of a cylinder center is relatively richer compared with that in the vicinity of a cylinder wall and the equivalent ratio gradually changes from the cylinder center to the cylinder wall.
These and other objects and features of this invention will be understood from the following description with accompanying drawings.